Direct chip attachment (DCA) of integrated circuit chips, to an underlying circuit board used in computers or the like presents several problems. Differences in coefficients of thermal expansion (CTE) between the chip, which is typically made of silicon, and the circuit board, which is typically made of organic material such as fiberglass filled epoxy often lead to failed connections. Also it is difficult to remove a chip that is directly attached to a circuit board during reworking if chip failure is noted during testing.
A number of solutions for connecting chips to circuit boards have evolved. In one such solution, the chip is connected to a chip carrier which in turn is connected to the circuit board. Employing carriers, especially with a CTE between that of the chip and that of the carrier, relieves the problems associated with differential coefficients of expansion and provides a modular component system that permits easy removal of a deficient chip from the circuit board during reworking of the board. Moreover, if the same material is used as a carrier as for the circuit board, the effect of CTE mismatch is minimized because the carrier is much smaller than the board.
One such carrier system, tape automated bonding (known as ATAB), often is used to connect I/C chips to circuit boards. An ATAB is comprised of a thin film of dielectric material, and a ground plane, typically a thin layer of copper, plated or laminated to the thin film. Atop the thin film, circuitization for connecting the I/C chip and distributing signals to and from the chip, has been laid. One or more I/C chips are attached to the top surface of the ATAB in accordance with the circuitization design. Plated vias are formed through the film to connect the top of the film of material to the bottom of the film of material. Attachment pads communicate with the vias on the ground plane surface but are electrically insulated therefrom. Solder balls are disposed on the pads for connecting the ATAB to the underlying circuit board.
Employing ATAB carrier technology improves the connection of the chip to the underlying circuit board and provides the convenience of modular parts. However, the ATAB carriers occupy additional space in relationship to the size of the chip when disposed on the circuit board. Thus, a large area of circuit board may be required to connect all of the necessary I/C chips. Also, ATABs do not remain flat; and this leads to warpage.
It would be desirable to have structures and methods for making structures that requires less surface area on the substrate for maintaining a given number of I/C chips using ATAB technology.